my current main goal on Splinterlands is not to purchase and upgrade cards but to increase the amount of SPS in my possession.

This is a goal I also have, but I'm still struggling to achieve it. Last month I did buy the dip when SPS went below .006 USD, but picking up missing alpha/beta cards to play in max wild events and ranked play is a hard habit to crack.

One thing going in your favor is your large bags of HIVE. I don't have nearly as much powered up and staked, but I do use all of my HP/HBD rewards to continue strengthening my position on Hive Blocks. If I were you, I might take my monthly HBD payout and swap it for SPS as a simple way to increase your SPS bags.

I've found that the @sps.dao tournaments are my best source of earning SPS. I can almost double my earned SPS each season just from the tournament events I play in. Plus, that SPS arrives unstaked and ready to be swapped for DEC or HIVE, so I find it slightly more challenging to stake the SPS prizes. Falling back into old habits, I usually end up buying more cards instead of buying more SPS.